We propose a scheme to generate maximally two-mode entangled state in a spinor-1 anti-ferromagnetic Bose-Einstein condensation. We reduce the three-level system into an effective two-level system via the quantum Zeno subspace created by exerting strong Raman coupling. We investigate the particle number evolution in the unreduced system to justify the existence of Zeno subspace and find that the effective system can be trusted and the entanglement production is reliable.